This invention relates to an improved magnetometer and more particularly but not by way of limitation to a self-resonant magnetometer for effectively sensing an external magnetic field.
Heretofore, one of the major noise problems in magnetic heading sensors was the ringing (oscillation) of the sense winding at its self-resonant frequency. In a second-harmonic type of magnetic sensor the sense winding oscillation produces a noise signal which is difficult to remove by filtering. The use of a digital driver and sensing techniques reduces this noise level by properly controlling the rise time of the driver signal.
This noise source was essentially eliminated when the drive circuit was operated at the self-resonant frequency of the sense winding. The sense winding signal is increased by its Q (its inductive reactance divided by its resistance). It was initially thought it would be impractical to design a circuit which would generate a stable sense winding frequency at its own resonance under all operational conditions. Each unit would have to be matched for the individual core characteristics which would also change with temperature. The above mentioned problems were eliminated by the subject invention.
In U.S. Pat. Nos. 2,480,265, 3,040,247, 2,565,799 and 3,626,280 various types of external magnetic fields are described having methods of biasing the magnetic core near saturation and methods of improving the accuracy using second-harmonic sensing. None of the above mentioned patents particularly point out the advantages, unique features and combinations of structure provided by the subject invention as described herein.